EnergyEnergy

• Energy – the ability to do workEnergy – the ability to do work

•• Kinetic – energy of motion, Kinetic – energy of motion,

anything that moves has kinetic anything that moves has kinetic energy.energy.

• K.E. = 1/2mvK.E. = 1/2mv22

• Potential – is stored energy, Potential – is stored energy, chemical or mechanical chemical or mechanical

• Law of Conservation of energy or law Law of Conservation of energy or law of conservation of matter and energyof conservation of matter and energy

• Matter and energy can not be Matter and energy can not be created or destroyed; it can only be created or destroyed; it can only be converted from converted from

• One form to another. E = mcOne form to another. E = mc2 2

Heat (q) is a measure of energy, in the metric system the unit of measure is a calorie. A calorie is the amount of heat required to raise the temperature of one gram of water one degree Celsius.

In the SI system the unit is a joule. 1 calorie = 4.184J

So heat is a measure of the amount energy while temperature is more of an Indication of the direction of flow of the energy. It always flows from the object

With the higher temperature to the lower one.

Specific heatSpecific heat

• Specific Heat – the amount of energy Specific Heat – the amount of energy needed to raise one gram of the needed to raise one gram of the material one degree Celsius. For material one degree Celsius. For water its 4.184j/(g.°C) or water its 4.184j/(g.°C) or 1c/(g.°C)1c/(g.°C)

• Calculating heat absorbedCalculating heat absorbed

• q = c x m x ∆T some q = c x m x ∆T some times ∆H is used in place of q times ∆H is used in place of q

• q is the heat change , c is the q is the heat change , c is the specific heat, m is the mass of the specific heat, m is the mass of the sample andsample and

∆ ∆T is the change in temperature of T is the change in temperature of the sample. the sample.

• Example Example

How much energy is required to How much energy is required to warm 250.grams of water from warm 250.grams of water from 20.0°C to 20.0°C to

100.°C for a cup of coffee?100.°C for a cup of coffee?

Q = 4.184j/g.°C x 250.grams x Q = 4.184j/g.°C x 250.grams x 80.0°C 80.0°C

Q = 83680 → 83700joules (to 3 sig Q = 83680 → 83700joules (to 3 sig figs )figs )

• You should be able to solve for any of You should be able to solve for any of the variables in the equation given the variables in the equation given the other three values or a way to the other three values or a way to find them.find them.

C = q / m x ΔT m = q / c x ΔT C = q / m x ΔT m = q / c x ΔT ΔT = q / c x m ΔT = q / c x m

Q = c x m x Q = c x m x ∆T∆T

m x ∆T m x ∆Tm x ∆T m x ∆T

Calorimetry - a method of determining the heat change of a chemical or physicl

change.Calorimeter – well insulated container used

in calorimetry.

Reactions can be endothermic, absorb energy or exothermic which release energy.

(Hypothermia )

Phase change graphPhase change graph

• HHf f = 334j/g Hvap = 2260j/g sph ice = 2.03j/g = 334j/g Hvap = 2260j/g sph ice = 2.03j/g • sph liq = 4.184j/g sph steam = 2.01j/g sph liq = 4.184j/g sph steam = 2.01j/g

Phase change graph and energies